A Surface Flux Scheme Based on the Monin-Obukhov Similarity for Finite Volume Models

Abstract

We proposed a surface flux scheme based on the Monin-Obukhov similarity for finite volume models. The scheme solves a negative bias existing in conventional surface flux schemes. In the conventional schemes, the model prognostic variables are used as the center point value in the model grid to estimate the surface fluxes even though the variables are volume-averaged values in finite volume models. The substitutional use of the volume-averaged model variables for the point value results in underestimation of friction velocity and temperature scale and consequent surface fluxes. The underestimation is more remarkable for a thinner layer, namely, higher resolution, and larger roughness length. In the proposed scheme, the model variables are used as volume-averaged quantities. Large-eddy simulation and single-column model experiments on a planetary boundary layer show that the surface fluxes calculated with the conventional scheme are, in fact, smaller compared to those with the proposed scheme. The proposed scheme allows better estimation of not only surface fluxes but also surface atmospheric diagnostics. Improved estimation of the surface flux with this scheme will contribute to improving the reliability of several kinds of simulations (e.g., those related to the atmosphere, ocean, ice sheet, and sea ice). Importantly, its impact becomes even more significant for higher-resolution simulations, which are likely to be more sought after in the future.